The identification and characterisation of key genes involved in somatic embryogenesis in wheat (Triticum, aestivum L.)

One of the most remarkable aspects of plants cells is that on application of the plant hormone auxin, they possess the unique ability to de-differentiate and return to embryonic development, via a process known as `somatic embryogenesis' (SE). On removal of auxin these totipotent cells are then capable of re-differentiating and regenerating into full adult plants. Although well characterised physiologically, the molecular mechanisms that regulate this important biological process are still very poorly understood. The research aim of this project was to improve our understanding of SE, by designing a series of cDNA microarray experiments to identify the genetic components responsible for the de-differentiation of somatic cells
to an embryonic state and the initiation, development and differentiation of somatic embryos towards adult structures. To achieve this aim, suitable embryogenic and
non-embryogenic systems were established and used for subtractive microarray analysis that has identified 701 differentially expressed genes that are specifically
related to SE in wheat. Following bioinformatic and expression analysis, 57 of these genes were short listed and further characterised by in situ hybridisation (ISH) to
provide further information of their temporal and spatial patterns of expression. A small subset of genes that demonstrated interesting patterns of expression, were
further characterised and functionally analysed via RNAi silencing studies. Here it is demonstrated that all of the genes tested for RNAi silencing results in a reduction of
the transformation and regeneration efficiencies. Furthermore the targeted silencing of several of these novel genes was shown to have an observable phenotypic effect on the development of somatic embryos and regeneration in wheat. Of particular interest is a wheat gene related to the rice embryo specific protein OSE 731, which appears to play an essential role in the transition of somatic embryos into differentiating adult structures. The silencing of this gene resulted in the continuous proliferation of somatic embryos (SEs) and arrested the development of these SEs into differentiated adult structures.